The present invention relates to a clamp apparatus for use in joining two members together at and around an annular joint interface therebetween, to a joining apparatus, and to a joining method. More particularly, the invention relates to a clamp apparatus used when a first member having a circular hole and a second member having a circular portion are joined together with the circular portion being fitted into the circular hole, at and around an entire annular joint interface between a circumferential wall of the circular portion of the second member and a circumferential wall of the circular hole of the first member, the clamp apparatus being adapted to clamp the second member so as to prevent movement of the second member in relation to the first member, as well as to a joining apparatus and a joining method.
Manufacture of industrial metal products for use in, for example, the automobile industry and the shipbuilding industry, may involve a step of joining together a first member having a circular hole and a second member having a circular portion fitted into the circular hole, at and around an entire annular joint interface between a circumferential wall of the circular portion of the second member and a circumferential wall of the circular hole of the first member.
Specifically, a known method of manufacturing a metal hollow member consisting of a base having a circular recess and a circular cover fitted into the recess and closing the opening of the recess is as follows. There are prepared the base having a circular recess and the cover to be fitted into the recess and to close the opening of the recess. A stepped portion is formed on the circumferential wall of the recess at an intermediate depth for allowing a circumferential portion of the cover to rest thereon. After the cover is fitted into the recess such that the circumferential portion thereof rests on the stepped portion of the recess, the base and the cover are joined together at and around an annular joint interface between the circumferential wall of the recess of the base and the circumferential wall of the cover by a fusion welding process, such as MIG (metal inert gas) welding, TIG (tungsten inert gas) welding, laser beam welding, or electron beam welding, or by a friction stir welding process.
In the fusion welding process, workpieces must be fixed against movement thereof in the course of joining, since the workpieces are subjected to pressure which is exerted on a molten pool at the time of melting or shield gas pressure, or to shrinkage force induced by welding heat. In the friction stir welding process, large force is exerted on workpieces when a probe is plunged into the interface between the workpieces and when the probe and the workpieces undergo relative movement; thus, the workpieces must be fixed more firmly than in the fusion welding process against movement thereof in the course of joining. In either case of the fusion welding process and the friction stir welding process, movement of workpieces in the course of joining causes impairment in dimensional accuracy of a product obtained by joining, or defective join.
Conventionally, in order to cope with the above problems, when a cover is to be friction-stir-welded to a base for forming a hollow member, the cover is provisionally and partially joined to the base by a general fusion welding process or a friction stir welding process (refer to, for example, Japanese Patent Application Laid-Open (kokai) No. 2002-248584).
However, since the method disclosed in the above publication includes an additional step for provisional joining, joining the cover to the base is rather troublesome. In the case where the cover is provisionally joined to the base at several points by a fusion welding process, a blowhole, cracks, lack of fusion, or a like defect is likely to arise. In order to avoid occurrence of such defect, preheating, treatment of craters, and the like must be sufficiently performed before main joining. This leads to an increase in the number of steps, thus impairing mass productivity.